Whenever and wherever food, in any form, is handled, processed, packed and stored, there will always be an unavoidable generation of wastewater. Wastewater is the most serious environmental problem in the manufacturing and processing of foods. Most of the volume of wastewater comes from cleaning operations at almost every stage of food processing and transportation operations. The quantity and general quality (i.e., pollutant strength, nature of constituents) of this processing wastewater generated have both economic and environmental consequences with respect to its treatability and disposal.
The cost for treating the wastewater depends on specific characteristics of it. Two significant characteristics that dictate the cost for treatment are the daily volume of discharge and the relative strength of the wastewater. Other characteristics become important as system operations are affected and specific discharge limits are identified (i.e., suspended solids). The environmental consequences in inadequately removing the pollutants from the waste stream can have serious ecological ramifications. For example, if inadequately treated wastewater were to be discharged to a stream or river, a eutrophic condition would develop within the aquatic environment due to the discharge of biodegradable, oxygen-consuming materials. If this condition were sustained for an extended period of time, the ecological balance of the receiving stream, river, or lake (i.e., aquatic microflora, plants, and animals) would be upset. Continual depletion of the oxygen in these waters would also give rise to the development of obnoxious odors and unsightly scenes.
Knowledge of characteristics of food and agricultural wastewater is essential to the development of economical and technically viable waste-water management systems that are in compliance with current environmental policy and regulations. Management methods that may have been adequate with other industrial wastewaters may be less feasible with food and agricultural wastewater unless the methods are modified to reflect the characteristics of the wastewater and opportunities it may hold. The waste-waters produced in agricultural processing and food processing vary in quantity and quality, with those streams from food processing typically having low strength and high volume and those coming from animal farming operations tending to have high strength and low volume. These differences in quantity and quality dictate the type and capacity of waste-water management systems that should be deployed.
A clear understanding of the characteristics of food and agricultural wastewater permits management decision on treatment and utilization methods that are effective and economical; this point is further spelled out in Table 1.1. For example, a low-strength, high-volume wastewater containing a small amount of organic colloidal particulates may require a stand-alone biological wastewater treatment facility or just a plate-and-frame filter press; the decision is both technical and economical. Another generalized observation is that the bulk of oxygen-demanding substances is in the liquid phase for food processing wastewater; most oxygen-demanding substances in the wastewater of a high-intensity livestock farming operation are in the form of solid particulates. Some food processing operations occur seasonally (processing of fruits and vegetables); this seasonality adds complexity to the wastewater management systems that handle different sources of food and agricultural wastewater year-round, and clearly the understanding of wastewater characteristics helps plan ahead for this abnormality of process operations. Knowledge of wastewater characteristics also allows strategic planning of water recycling and reuse and recovery of valuable components in the wastewater.
As in most wastewaters, the components present in agricultural and food wastewater run a gamut of many undefined substances, almost all organic in nature. Organic matters are substances containing compounds in possession of mainly elements C, H, and O. The carbon atoms in the organic matters (also called carbonaceous compounds) may be oxidized both chemically and biologically to yield CO2 and energy. It is possible that some sources of wastewaters from certain food processing operations in a processing plant may have limited numbers of possible contaminants present; however, these wastewaters tend to mix with other streams of wastewaters
Table 1.1. Wastewater treatment options available to remove various categories of pollutants in food and agricultural wastewater.
Pollutants in Wastewaters
Dissolved organic species Dissolved inorganic species
Suspended organic materials
Suspended inorganic materials
Biological treatment; adsorption; land applications; recovery and utilization Ion exchange; reverse osmosis; evaporation/
distillation; adsorption Physicochemical treatment; biological treatment; land applications; recovery and utilization Pretreatment (screen); physicochemical treatment (sedimentation, flotation, filtration, coagulation)
from the same work site, making it virtually impossible to catalog the substances in the effluents from the plant. Thus, the characteristics of agricultural and food wastewater can be viewed as a set of well-defined physico-chemical and biological parameters that are critical in designing and managing agricultural and food wastewater treatment facilities.
General characteristics of wastewaters in agriculture and food processing
Wastewater from food processing operations is defined by the food itself. Food and agricultural wastewater contains dissolved organic solids from various operations and debris from mechanical processing of foods, such as peeling and trimming, and hydrodynamic impacts in washing and transporting. Agricultural and food processing operations inevitably use large quantities of water to wash—and, in some instances, cool—food items. Canning wastewaters are essentially the same as home kitchen waste because the wastewater is accumulated from various processes involved in the canning operations, such as trimming, sizing, juicing, pureeing, blanching, and cooking. Vegetables also require large amounts of water to blanch and cool. Almost all operations in food or agricultural processing involve cleaning plant floors, machinery, and processing areas; the water used is often mixed with detergents that sometimes are doubled as lubricants for the food processing machinery.